Control valves are an integral part of most railway freight cars. The control valve operates to control the flow of air to and from the brake cylinders and to charge the auxiliary and emergency reservoirs. An important part of such control valves are limiting valves.
The service portion of such control valves contains two brake cylinder limiting valves which function to limit the maximum pressure directed to the brake cylinder application pipe or brake cylinder relay valve control pipe during service or emergency brake applications. The limiting valves are designated as the "Service Limiting Valve" and the "Emergency Limiting Valve". The maximum pressure output from these limiting valves is predetermined by load settings on the springs within each valve.
Such limiting valves rely on diaphragms to perform their function. A metal insert is mounted on such diaphragms and is held in place by the use of an adhesive. One problem with the present technology is that the diaphragm tends to delaminate at the periphery of the metallic insert because this is a stress concentration point which leads to delamination as the diaphragm flexes during operation. When delamination occurs, the diaphragm becomes inoperable and must be replaced before the limiting valve can operate properly again. Occurrences of this type are considered premature failure of the diaphragm and result in down time and further expense for the railroad. Thus, any improvement to the diaphragm that will eliminate premature failure and extend the useful service life of the diaphragm is desirable.